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The 2009 Audi S4 sedan finally comes close to actually satisfying all of our expectations of an Audi S car, even on track day.

We get just as excited as anyone when we drive an Audi RS6 with that awesome turbocharged V10 mojo. But given current needs, the Audi V10 can seem like heinous overkill, and indeed such engines have a problematic future, regardless of said overkill's sweetness.

Meanwhile the S-line of Audi variants hasn't been too thrilling up until now. It's been good stuff, but more like luxury trim matched with big horsepower, like an old-fashioned Mercedes-Benz. Even the Audi S5 with its perennial 4.2-liter Audi V8 has fallen short of our expectations for suitable S-line specialness.

Given this, it says a lot that the new 2009 Audi S4 sedan has busted through our wall of skepticism. There's no twin-turbo V10, but it's got a real engine. And this time the S-line designation really means something.

Supercharging Returns to AudiThe 3.0-liter V6 TFSI engine in the new Audi A6 range is the first supercharged Audi engine in several decades. In standard form, the Roots-type Eaton supercharger provides max boost pressure of 11.6 psi, delivering 285 horsepower and 310 pound-feet of torque for the A6. For the 2009 Audi S4, this same engine with the same boost results in 329 hp and 324 lb-ft of torque. With the standard six-speed Getrag manual transmission in place, this power gets the S4 sedan to 100 km/h (62 mph) from a stop in just 5.1 seconds, while the optional S tronic seven-speed dual-clutch transmission gets you there in 5.3 seconds. Which is plenty quick either way.

The supercharger here is almost identical to the four-lobe unit used for the 2009 Cadillac CTS-V. On the quaint, narrow roads of Mallorca and during several heated laps of the local racing circuit, the clear benefits of supercharged power could not be denied. While you're best off keeping revs up in the sweet spot over 2,900 rpm where all the torque kicks in, most of the power is available from way down low thanks to the no-lag raison d'être of a supercharger.

After the massive deceleration customarily required to set up any heavily understeering, all-wheel-drive Audi for correct entry into a curve and then properly set up for full hookup from all four tires upon exiting said curve, turbo lag and surge are not quite what you want when you hit the throttle. The quick surge of response from a supercharger does this trick in far better style.

Shifting ParadigmsFor North America, buying preferences for manual transmission versus S tronic is surprisingly 50/50, the Audi people tell us. After both tearing it up and cruising meekly using both, we give the six-speed manual the ever-so-slight edge. With the manual, the car loses a noticeable 77 pounds mostly off the front end, reducing overall weight to 3,638 pounds (some 231 pounds less than the previous S4). The shifts catch quickly, and we could hear the supercharger just enough to feel like a badass. We could do with less throw on the shift lever, but we cannot slight the shift action itself.

Meanwhile, this seven-speed S tronic is Audi's first dual-clutch transmission joined to a longitudinally positioned engine, not to mention the company's first dual-clutch unit that's designed to withstand serious torque. Of course, the transmission's action reduces supercharger whine to a whisper except for a brief interlude between 2,000 rpm and 3,000 rpm at full throttle, and that's no fun. We'd like much larger shift paddles and a more assertive sense of crisp shifts, but the system works very well all the same.

Opting for the $2,900 Audi Drive Select (ADS) system gives the S4 pilot a choice between the usual Comfort, Auto and Dynamic setups for recalibrating the throttle response, shift timing (for S tronic), steering assist and suspension feel. For the S4, this system also features Individual mode, which can be altered through the MMI control interface to mix and match all of these parameters to customize the setup you prefer. There is also the ability to switch off stability control completely, or to keep just the anti-skid recovery (ASR) function to monitor sideways sliding for you.

More Like RWD Is More Like ItAt least once during every drive of a hot-rod Audi S, R, or RS model, we ask the Question, as in: "Will Audi ever give in and make us a rear-driver performance car with the engine up front?" In response this time, Peter Schwarzenbauer of the Audi management board told us, "Never. Not while I'm here, at the very least."

So, rather than invest in a rear-wheel-drive platform that can turn an Audi into a BMW, Ingolstadt has done everything it can to urge its heavy, high-performance all-wheel-drive cars to let us have more fun during more technical driving — that is to say, something more than the usual lack of decent turn-in followed by mad understeer. In this case, the 2009 Audi S4 introduces the company's pretty good solution.

For around $900 (and well worth it), you can equip your S4 with a rear-mounted sport differential supplied by Magna in Austria. Much like the recently introduced rear differential for the Haldex all-wheel-drive system used by Saab and the new all-wheel-drive BMW xDrive solution, the Magna differential shifts torque across the rear wheels, accelerating the outside rear wheel to push you through a curve proactively instead of just waiting around for stability control to poop on the party.

We got our best results by disabling the stability control and anti-slide-recovery electronics, dialing the ADS configuration to Dynamic and just going for it. Thanks to an overall ride height that's 0.8 inch lower than that of the A6, the optional 19-inch wheels with harder Dunlop tires, Audi's newest steering with just 2.2 turns lock-to-lock, 80 percent of the engine torque going to the rear wheels (40 percent front/60 percent rear is the usual split), stiffer springs, more tire camber and steering caster, and quick supercharged engine response (whew!), the 2009 Audi S4 attacked the track and rural roads with uncommon zeal for a car based on the cooking A4.

This car can still understeer, but it now has a chassis that's up to clubsport-style antics. Of course, if you could equip an A4 with a 25:75 bias Quattro setup with the extreme possibility of a 5:95 split and then peel off another 200 pounds yet, such a car could be a legend. For now, though, the 2009 Audi S4 is sweet progress.

Fierce and FrugalEven though the S4's supercharged V6 encourages you to seek its 7,000-rpm redline and its exhaust note puts us in mind of a double-barreled fat-bore V8, Audi is estimating this car with a manual transmission will achieve 17 mpg EPA city and 32 mpg EPA highway in the U.S. The S tronic car coaxes 1 mpg more from the highway rating.

Audi itself reckons that this supercharged V6 delivers 30 percent better fuel economy than the 4.2-liter V8. Carbon-dioxide emissions ratings are way down here versus the V8 as well, to the tune of 21 percent.

It's the way of the future. Get used to it.

Hurry Up! No, Wait!While the U.S. might be Audi's fourth-largest market in total sales, we are receiving 3,000 S4s (all sedans) of the expected 7,000 units (both sedans and Avant wagons) that are scheduled for production next year. So we're No. 1! Except that we'll have to wait until August 2009 for deliveries to start, so maybe we're not.

The estimated $49,000 base price for the new Audi S4 sedan represents only a modest price increase against the outgoing S4. Not a single S4 will be sold for less than $55,000, however, given the desirable cost options list (which unfortunately does not include 20-inch wheels, which are reserved for the S5). Every 2009 Audi S4 will have a sunroof, though, so make certain you're not too, too tall.

Edmunds attended a manufacturer-sponsored event, to which selected members of the press were invited, to facilitate this report.